FSpaceRPG article

Sometimes, knowing the air pressure at altitude on Earth (or equivalent 1G worlds) is handy.

This calculator uses a roughly exponential drop with altitude compared to 1 Atmosphere at sea level. It is not suitable for use on planets with differing sizes, surface gravities, atmospheric composition and pressures.

Oter factoros such as temperature, gas composition, humidity and weather conditions can all affect resultant atmospheric pressure. Use this as a basic guide for Earth.

For humans, the lowest tolerable breathing pressure of standard Earth air is about 0.47 atm (475 millibars of atmospheric pressure) - recorded typically at 5950m altitude. Pulmonary and cerebral edema that leads to death occurs at about 0.35 atm (less than 356 millibars). With a pure oxygen breathing apparatus (100% oxygen instead of 21% at sea level), roughly around 12.2 percent sea level air pressure or 121.7 millibars, a human can still breath without ill effects. Below around 6 percent sea level pressure, or 61.8 millibars the water and blood in the human body starts to boil.

Oxygen supplies, pressure and vacuum suits all help mitigate the effects of increasing altitude and lower pressure.